1. Does your group have what it takes to build a bridge?
BRIDGES
Does your group have what it takes to build a bridge?
Bridges have been used for centuries to cross, streams, rivers and valleys to make it easier for people to transport them.
The following links will give you more information on the History of Bridges in the British Isles
Follow Link
List alternative uses for Bridges from the website.

2. BRIDGES Types of Bridges Beam Bridge
The word "beam" comes from the old English word for tree. The first bridges were probably logs.
"Pier": the bridge support.
How high do you make the piers? That depends on what has to travel underneath.
"Span": the distance pier to pier.
The span depends on the strength and weight of the beam. The thicker the material, the more weight it will hold and the further the span. But the thicker the material, the heavier the bridge, so the more it takes to hold it up. A very strong beam could be too heavy for the "span" and sag into the river. We can lighten the beam by using a truss

3. Can we make the span longer
BRIDGES
Can we make the span longer
Cantilever Bridge
There is a type of Beam Bridge called a cantilever. It is related to a lever.
Imagine if one end of a lever, balancing on a fulcrum, were anchored to the ground. The other side could hold considerable weight.
Suppose there were two levers on each side of a gap, each with one end fixed to the ground, something like two diving boards extending from the opposite banks of the river. Then, a centre beam could be balanced across these "diving boards." The fixed levers would be able to hold up the centre beam. In this way, a cantilevered bridge can span a wide river.

4. BRIDGES Arch Bridge Bridge of the Isles, Scotland.
Arches are made up of wedges and a "keystone," the wedge at the top. An arch bridge stands up with "push." The "push" is in the form of a curve. Arch bridges can be very wide because you can have arch after arch in a continuous line.
If the arch were very shallow, you would need to anchor the bottom wedges to the ground. This is usually done with a supporting wall.
To show the principle of compression or "push" pick up, from a shelf, five or six books by pushing against the end books and lifting. The books stay together because you are exerting a "push." Can you place another book on top of the row? It depends on how hard you exert the pressure against the end books.
Bridge of the Isles, Scotland.

5. BRIDGES Suspension Bridge .
Suspension bridges are really arch bridges turned upside down, but they hold together with tension or "pull" instead of "push," like the arch bridges. They can span much greater distances than any other type of bridge.
Suspension bridges are very flexible, which is not a problem, as long as the swaying of the bridge is not in rhythm with repetitive gusts of wind. Then the swaying could build and build, until finally the bridge disintegrates. .

6. BRIDGES What shape is the Strongest? Triangles Squares Pentagon Tubes.

7. BRIDGES
Activity 1
Using the plastic Building materials, build the following shapes. Push or pull the corners and answer the questions shown on a sheet of paper.
TRIANGLE RECTANGLE SQUARE .
Sketch each shape and comment if they changed shape and why?

8. BRIDGES Activity 1 Cont Build a Pentagon. Pentagon .
Sketch the Pentagon and comment if it changed shape and why?

9. BRIDGES
Activity 2
Place the triangle on the bench top. Hold down at B and C and push as shown.
Explain what happens
Hold down A push in the middle between B and C .

10. BRIDGES Activity 3 Build and test the frame shown
Did the string stay tight?
Turn the frame to the new position shown below .

11. BRIDGES
Activity 3
A Member being pulled apart is said to be in TENSION and is called a TIE.
A Member being pushed together is in COMPRESSION and is called a STRUT. .

12. BRIDGES ACTIVITY 4 . Join the P5s to form a square frame.
Fit the P6 to form a diagonal for the frame
Test as shown.
Did the square frame, with its diagonal, change shape? .

13. BRIDGES ACTIVITY 5 – Extension .
Take component P1 (flat beam), support it as shown and apply a push in the direction of the arrow at the mid point.
Did the beam bend easily in the direction of the arrow?
Take the same component, support it as shown and apply a push in the direction of the arrow at the mid-point.
Did any other bending or twisting tend to take place?
Did you have any difficulty in keeping the beam steady? .

14. BRIDGES
Activity 7 Ext
Take the P2 and fit the P1s as shown. Make sure that the small raised pins in the centre of the P2 fits into the notches of the P1s.
Support the beam as shown with P2 uppermost. Push in the direction of the arrow at the mid point.
Did the beam bend easily in the direction of the arrow?
Did any other bending or twisting tend to take place?
Did you have difficulty in keeping the beam steady?
Is the channel beam an improvement on the angle beam in supporting the load? .

15. BRIDGES This type of beam is called a CHANNEL BEAM or U BEAM.
If the beam is totally enclosed in the form of a square or a rectangle then it is called a BOX BEAM. .

16. BRIDGES
Activity 8
Take the P2 and fit the P4 (60)s as shown. Make sure that the small raised pins in the centre of the P2 fit into the notches of the P1s.
ISupport the beam as beam as shown with P2 uppermost.
Push in the direction of the arrow at the mid point.
Did the beam bend easily in the direction of the arrow? .

17. BRIDGES This type of beam is called a CURVED CHANNEL BEAM.
It is used on many iron bridges, such as the one shown in the illustration below.
Steel arch spandrel design: Sydney harbour bridge, Australia, with a span of 500m .

18. BRIDGES
SUMMARY:
The triangle resists, but the square and pentagon collapses; unless the angles are braced. You could create a brace for the square by constructing a diagonal - which, in effect, is making two triangles.
The triangle is the strongest shape. Triangles are used to make a very strong form called a truss. Flat structures like the ones you have tested are called FRAME structures.
Another very strong shape is a tube. Think about bicycle frames and bamboo shoots. .

19. Forth bridge triangular truss system
BRIDGES
What is a truss?
Beam bridges can span a greater distance with a thicker beam. But there is a limit, because too thick a beam will sag into the river. An alternate solution is to build a beam of triangles, a "truss," which is much lighter than a beam of similar thickness. A truss is extremely strong and stable.
Forth bridge triangular truss system .

20. BRIDGES
Does the bridge material make a difference in the strength of the bridge?
Shape is important for strength, but so is the material. A steel beam will hold more weight that a wooden beam of equivalent size. Today, bridges are built of steel and reinforced concrete.
Reinforced concrete beams are created by placing steel bars into the concrete before it hardens. This skeleton of steel helps the concrete withstand the tension that develops when long, unsupported beams are subjected to bending under heavy weight loads. .

21. BRIDGES
THE CN Tower
The CN Tower, in Toronto, at 553 metres, is still the tallest free-standing structure in the world.
How was this tower built?
Construction engineers used a slip form. Vertical rods were put into place; a mould was built around these rods and the concrete was poured. When the concrete had hardened enough to support weight, the mould (slip form) was pushed vertically up the rods, and more concrete was poured. This process was repeated again and again until the desired height was attained. . .